So much has been written about livestock cycle theory that it seems bold to try again bringing some new light on the subiect. This was however the first intention of my dissertation. Two points appeared to me as deserving more attention. First no economic model of livestock supply has ever included a demographical part expressed by a dynamic complete model in the line of human popu'lations. Since I had studied the properties of such a model Ijntented to analyse hog supp'ly in these terms, by plugging in control variables related to supply behavior of hog producers. This turned out to be unfeasible for lack of detailed data on inventories of hogs on farm in France, which were necessary to set up the model in a demographjc framework. The only data available over a long enough period of time, concern slaughtered hogs. I had therefore to give up this approach, which would have led also to some particular estimation problems. The second point I wanted to study in a systematic manner, was the implications of the relationship between inventories and slaughtered hogs at each point i.n time, arelationship which comes up naturally when the demographic approach is used.